Technological Field
The present invention relates to an image forming apparatus that forms an image by transferring a toner image to a sheet to fix.
Description of the Related Art
In related art, an image forming apparatus that forms an image on a sheet using toner is known. In such an image forming apparatus, a correcting unit including a registration roller that corrects inclination of the sheet, deviation of a position in a width direction of the sheet in a main scanning direction of the image, a transfer unit that forms an image on the sheet, and a fixer that fixes the image formed on the sheet by the transfer unit.
In the correcting unit provided with the registration roller, the deviation of the sheet is corrected by moving the registration roller that nips the sheet in an axial direction. In operation of moving the sheet in the width direction, in order to reduce resistance of movement of the sheet, it is configured such that a roller on an upstream side of the registration roller is separated from the sheet. Also, after correcting the deviation of the sheet, operation of separating the registration roller from the sheet and returning the same to an initial position is performed. In this manner, on the upstream side of the transfer unit, the roller that conveys the sheet is separated from the sheet.
In the image forming apparatus, occurrence of paper wrinkling by a fixing roller and image bending is inhibited by adjusting alignment of the registration roller, a transfer roller forming the transfer unit, and the fixing roller forming the fixer. However, difference in roller diameter between front and back and the like due to roller accuracy at the time of exchange of the fixing roller and the like, assembling accuracy, uneven wear and the like occurs with time.
Therefore, an alignment adjusting mechanism of a fixer that adjusts a position in a conveying direction of a sheet and a vertical direction orthogonal to the conveying direction by using a motor and a solenoid is suggested (refer, for example, to JP 2000-242124 A).
However, the alignment adjusting mechanism provided with a driving mechanism such as the motor and the solenoid has a large number of parts and a complicated structure, so that a product cost increases.
Also, while the sheet is nipped to be conveyed by the registration roller, the sheet is inhibited from bending during conveyance, and bending of the image to be formed on the sheet is inhibited. However, when the registration roller loses contact with the sheet because the registration roller separates from the sheet for returning to its initial position or a rear end of the sheet passes through the registration roller, there is possibility that the sheet bends during the formation of the image under an effect of the inclination, deformation and the like of the fixing roller.
When the sheet bends during the formation of the image, the image formed on the sheet bends and a quality is deteriorated. In recent years, demand is increasing also for sheets referred to as long paper larger than a size that may be accommodated in a paper feed cassette. However, a sheet such as the long paper which is long in the conveying direction tends to be remarkably bent on a rear end side especially before image formation, and bending of the image is noticeable.